feat(metrics): record commit_source on the Committed metric

Add nullable position 18 (`commit_source`) to `CommittedValues`, mirroring
`CheckpointValues::checkpoint_type`, so analytics can tell commits the
daemon attributed on the traced path (null) from commits attributed later
from their reflog record (`untraced_fixup`, emitted by the upcoming fixup
pass). `PostCommitOptions` carries the value into `record_commit_metrics`;
the daemon's recovery-timestamps entry point now takes the options struct
directly instead of two loose flags.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>